Tibbetts' Murderer Pleads Not Guilty — Claims He Blacked Out

Rivera, 24, was arrested and charged with first-degree murder on Aug. 21 after police searching a cornfield about 12 miles southeast of Brooklyn discovered the body of Tibbetts, a 20-year-old University of Iowa student.

Prosecutors allege Rivera abducted Tibbetts while she was out for an evening run, killed her and disposed of her body in the secluded location.

Authorities announced last month preliminary autopsy results from the state medical examiner's office showed Tibbetts was the victim of a homicide and died from "multiple sharp force injuries."

A criminal complaint alleges Rivera confessed to authorities during a lengthy interrogation, saying he drove his car to follow Tibbetts' jog, eventually got out on foot to talk to her and then chased after her. Rivera told investigators he panicked after Tibbetts threatened to use her cellphone to call police. He claims he blacked out at that point and later came to as he was unloading Tibbetts' bloody body from the trunk of a car, according to the complaint.